One objective of this research is to determine the relationship between rod and cone ERG recovery and the concentrations of rod and cone visual pigments during dark adaptation of the isolated perfused frog retina. This will be done by simultaneously measuring the ERG and visual pigment concentrations during dark adaptation. Rhodopsin concentration is measured by means of spectrophotometry and principal cone pigment concentration is measured with the early receptor potential (ERP). A further objective is to study the regeneration of cone pigment in the isolated retina and to study the effect of photoproducts of bleaching on ERG sensitivity. Adaptation will also be studied in the lateral geniculate nucleus (LGN) of the cat. The objectives in these experiments are to 1) determine how the response-intensity functions of single neurons in he LGN are affected by adaptation at both scotopic and photopic levels of adaptation, 2) compare adaptation in the LGN and optic tract (OT); 3) determine the effects of adaptation on the transient and sustained cells in the LGN, and 4) determine the absorption spectrum of the cat's long-wavelength cone pigment.